Yeast provides a flexible and rapid genetic system for studying
cellular events. With an approximate generation time of 90 min, colonies
containing millions of cells are produced after just 2 d of growth. In
addition, yeast can propagate in both haploid and diploid forms, greatly
facilitating genetic analysis. Like bacteria, haploid yeast cells can be
mutated to produce specific nutritional requirements or auxotrophic genetic
phenotypes, and recessive lethal mutations can either be maintained in haploids
as conditional lethal alleles (e.g., temperature-sensitive mutants), or in
hetero zygotic diploids, which carry both wild-type and mutant alleles.